US-20260126324-A1 - TRANSPARENT CERAMIC WINDOWS FOR HYPERSONIC APPLICATION

Abstract

In an approach to synthesizing transparent ceramic windows, a powder is synthesized. A green body is fabricated from the powder. The green body is densified.

Inventors

• Krenar Shqau
• Amy Marie Heintz
• Erica S. Howard
• Ian Haggerty
• Phil DENEN

Assignees

• BATTELLE MEMORIAL INSTITUTE

Dates

Publication Date

20260507

Application Date

20231004

Claims (20)

1. 1 . A process to synthesize transparent ceramic windows, the process comprising: synthesizing a powder; fabricating a green body from the powder; and densifying the green body.
2. 2 . The process of claim 1 , wherein synthesizing the powder further comprises: condensing a precursor solution to form a gel; reducing the gel by evaporation; and pyrolyzing the gel to complete crystallization of the gel into the powder.
3. 3 . The process of claim 1 , wherein the powder is beta silicon carbide (β-SiC).
4. 4 . The process of claim 1 , wherein fabricating the green body from the powder further comprises: dispersing the powder in a colloidal stabilizer using ultrasonic dispersion; draining a dispersing media from the colloidal stabilizer; removing volatile organic compounds from the colloidal stabilizer; and filtering the colloidal stabilizer to remove foreign particles to yield a separated and stabilized solution.
5. 5 . The process of claim 1 , wherein fabricating the green body from the powder further comprises: dispersing the powder in a dispersing media; and draining the dispersing media.
6. 6 . The process of claim 5 , wherein the powder is dispersed using ultrasonic dispersion.
7. 7 . The process of claim 5 , wherein the dispersing media is a colloidal stabilizer.
8. 8 . The process of claim 5 , wherein the dispersing media is drained using vacuum filtration.
9. 9 . The process of claim 1 , wherein densifying the green body further comprises: using a rapid thermal treatment to densify the green body.
10. 10 . The process of claim 9 , wherein the rapid thermal treatment is spark plasma sintering.
11. 11 . The process of claim 10 , wherein the spark plasma sintering is performed at a temperature below 1500 degrees Celsius.
12. 12 . The process of claim 1 , wherein densifying the green body further comprises: loading the powder into an electrically conducting die; and sintering the powder under a uniaxial pressure.
13. 13 . The process of claim 1 , wherein the green body has a density of at least 60%.
14. 14 . A process to synthesize transparent ceramic windows, the process comprising: condensing a precursor solution to form a gel; reducing the gel by evaporation; pyrolyzing the gel to complete crystallization of the gel into a powder; dispersing the powder in a colloidal stabilizer using ultrasonic dispersion; draining a dispersing media from the colloidal stabilizer; removing volatile organic compounds from the colloidal stabilizer; and filtering the colloidal stabilizer to remove foreign particles to yield a green body; loading the green body into an electrically conducting die; and sintering the powder under a uniaxial pressure.
15. 15 . The process of claim 14 , wherein the powder is beta silicon carbide (β SiC).
16. 16 . The process of claim 14 , wherein sintering the powder under the uniaxial pressure further comprises: using spark plasma sintering.
17. 17 . The process of claim 16 , wherein the spark plasma sintering is performed at a temperature below 1500 degrees Celsius.
18. 18 . The process of claim 14 , wherein the green body has a density of at least 60%.
19. 19 . The process of claim 14 , wherein the powder is dispersed using ultrasonic dispersion.
20. 20 . The process of claim 14 , wherein the dispersing media is drained using vacuum filtration.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a National Phase application filed under 35 USC § 371 of PCT Application No. PCT/US23/75899 with an international filing date of Oct. 4, 2023, which claims the benefit of the filing date of U.S. Provisional Application Ser. No. 63/378,438, filed Oct. 5, 2022, the entire teachings of which is hereby incorporated herein by reference. TECHNICAL FIELD The present application relates generally to ceramic materials and, more particularly, to transparent ceramic windows for hypersonic applications. BACKGROUND Many aircraft, such as airplanes, helicopters, unmanned vehicles, and missiles (e.g., infrared (IR) seeking missiles), include a seeker that utilizes IR radiation to track one or more targets. In the example of a missile, the seeker typically includes an IR sensor that is positioned within the body of the missile (e.g., in the nose cone) and oriented to detect IR radiation through a ceramic window that is at least partially transparent to such radiation. The transparent ceramic window can be subject to very high heat loads from the compressed air during flight, resulting in a significant temperature gradient across the window. That temperature gradient can impart significant thermal stresses to the window, potentially leading to failure of the window and destruction and/or malfunction of the aircraft. There is a need for aircraft capable of hypersonic flight at speeds ranging from Mach 1 to Mach 20 that include IR tracking capability. At such operating conditions, the transparent ceramic window will be subject to high heat loads as the speed of the aircraft increases. If the transparent ceramic window cannot withstand such conditions, it may catastrophically fail, resulting in loss or malfunction of the aircraft. Existing transparent ceramic window materials such as sapphire and aluminum oxynitride have been studied as potential materials for use as a hypersonic IR window due to their good thermal resistance and transparency to IR radiation in wavelength ranges of interest. However, such materials do not perform well as an IR seeker window at hypersonic conditions due to the thermal shock (temperature gradients in the material) that is imposed on the material during flight at such conditions, which can impose thermal stress on the window that exceeds the strength of such materials. BRIEF DESCRIPTION OF THE DRAWINGS Reference should be made to the following detailed description which should be read in conjunction with the following figures, wherein like numerals represent like parts. FIG. 1 is an example of the impact of light scattering mechanisms on the transparency of polycrystalline ceramic windows. FIG. 2 is a Venn diagram representing some of the defects that may reduce the optical transmittance of polycrystalline ceramics. FIG. 3 is an example graph of the effect of grain size on the light transmittance of polycrystalline ceramics. FIG. 4 is an example graph of process temperature versus the rate of grain growth in the manufacture of polycrystalline ceramics. FIG. 5 is a Venn diagram representing some of the factors affecting overall ceramic properties of polycrystalline ceramics. FIG. 6 is an example block diagram illustrating factors affecting the final sintering process, consistent with the present disclosure. FIG. 7 is an illustrative example of one embodiment of a process flow for manufacturing transparent ceramic windows for hypersonic applications, consistent with the present disclosure. FIG. 8 is a flow chart diagram of workflow 800 depicting operations for the synthesis of a transparent ceramic window for hypersonic applications, in accordance with an embodiment of the present disclosure. FIG. 9 is an illustration of a colloidal process, consistent with the present disclosure. FIG. 10 is an illustration of a colloidal process using vacuum filtration, consistent with the present disclosure. FIG. 11 demonstrates the effect of the sintering temperature on grain growth. DETAILED DESCRIPTION The present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The examples described herein may be capable of other embodiments and of being practiced or being conducted in various ways. Also, it may be appreciated that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting as such may be understood by one of skill in the art. Throughout the present description, like reference characters may indicate like structure throughout the several views, and such structure need not be separately discussed. Furthermore, any particular feature(s) of a particular exemplary embodiment may be equally applied to any other exemplary embodiment(s) of this specification as suitable. In other words, features between the various exemplary embodiments described herein are interchangeab